To enumerate king Asoka's successors, Taranatha has followed an old Buddhist quasi-historical text Manjusrimulakalpa. Manjusrimulakalpa (Mmk) lists king Asoka's successors as Visoka (=Vigatasoka of Taranatha), Surasena (=Virasena of Taranatha), Nanda, Chandragupta, and Bindusara. Another variant of king Virasena found in Taranatha's account itself is Indrasena. Scholars have restored king Virasena of Taranatha with king Surasena mentioned in the Manjusrimulakalpa. Dr K. P. Jayaswal, Dr N Dutt etc have also identified Asoka of Manjusrimulakalpa with Kalasoka (of Saisunaga dynasty) mentioned in the Mahavamsa. Further, Nandivardhana, son of Kalasoka of Saisuanaga dynasty has been identified with Visoka or Vagatasoka of Taranatha. Thus, the Manjusrimulakalpa list of kings of Central India (Magadha) actually starts with Saisunaga kings, covers the Nanda kings and ends with Mauryas Chandragupta and Bindusara.
King Surasena, (misquoted by Taranatha as Virasena or Indrasena), was succeeded by his son king Nanda who ruled Central India (Madhyadesa) i.e Magadha for 29 years. This Surasena of Manjusrimulakalpa has been identified with Nanda king Ugrasena (founder of Nanda dynasty) mentioned in Mahabhodivamsa, or Nanda king Mahapadamapati of the Puranas. Taranatha also mistook the name Mahapadama Nanda for two personages Nanda and Mahapadama and made the latter son of the former; or it may be that Nanda took appellation of Mahapadama sometime after commencement of his reign. It is noteworthy that Taranatha's Virasena (restored as Surasena by later scholars) was the king of Magadha and not of Gandhara as was erroneously supposed by Dr F. W. Thomas. Thus, it was this wrong interpretation of Tarantha's account by Dr F. W. Thomas which has led him to erroneously identify Virasena of Tarantha with Vrishasena of Divyavadana and derive erroneous conclusion that Virasena was a Maurya ruler of Gandhara and king Subhagasenna was probably his son/successor who later succeeded Virasena as the ruler of Kabul valley. Also in the light of above facts, Dr Thomas' equation to relate Vrishasena of Divyavadana with Virasena of Taranatha automatically loses it argumentative weight since Virasena was misquoted by Taranatha for king Surasena of Central India. Many scholars have, however, accepted Dr Thomas’s hypothesis without critical scrutiny. Interestingly, some scholars also identify Virasena of Taranatha variously with the later Maurya king Suyasas (son of Asoka) or with Jalauka (son of Asoka) or with Salisuka or with Somasarman. There are even some who say that Sophagasenus was the epithet worn by king Asoka himself. Louis de La Vallée-Poussin holds that Sophagasenus which translates to Subhagasena may be considered to be the father of Virasena, which does not however bear scrutiny. As can be seen from the known facts of history and from the chronological order of kings given in Manjusrimulakalpa as well as by Taranatha, it is hard to believe the list given in Taranatha's History. Thus, Taranatha’s list of Asoka’s successors is obviously erroneous, commingled and confused. Commenting on Taranatha's accounts in respect of Asoka, Dr V. A. Smith observes that Taranatha’s account is hopelessly confused. Sir Charles Elliot has also branded Taranatha’s account as confusing and untrustworthy. Susan L. Huntington too comments on Taranatha’s history and calls it unreliable. Thus, we can not put too much reliance on Taranatha’s account on Asoka and his successors.
Lastly, Polybius's reference to "renewal of friendship" indicates that Sophagasenus must have come to the throne some years prior to 206 BCE. The existence of at least one independent kingdom in north-west before BCE 206 shows that Maurya empire must have begun to break-up nearly a a quarter century prior to usurpation of Magdhan throne by Pushyamitra in 185 BCE.
Maurya Empire declined after 232 BCE, after the strong arm of Asoka was withdrawn on his death. His successors were unable to keep possession of the outlying regions including Kamboja (Kabul/Kunar valleys), Yona (Arachosia) and western Gandhara (Peshawar valley). These areas were inhabited by martial and freedom loving self-ruling people who seldom easily yielded to foreign control. Already during the heydays of Maurya empire, three revolts had occurred in eastern Gandhara alone-- two during reign of Bindusara and one during later years of king Asoka. We do not have any surviving records of the political conditions in the regions west of river Indus including Kamboja, but it is not too difficult to visualize that the areas west of Indus were even more impatient of foreign control. Not long ago, the same Ashvakas had assassinated Nicanor, the Greek Strap of Massaga in 326 BCE while Alexander was still in Punjab. Asoka’s Rock Edicts V and XIII amply prove that the nations of Kamboja, Yona, Gandhara (i.e. western Gandhara) etc were semi-sovereign and were ruled by their own community chieftains who enjoyed a feudatory status under the Mauryas. The 'Ŕāja-Vişayas' of king Asoka's thirteenth Rock Edict, which include the Kambojas, Yonas, Nabhika, Bhojas, Andhras etc, were "the soverign (self-ruling) states within the Maurya Empire". M Boyce writes: "The Kambojas enjoyed a measure of autonomy...and were governed in some measure by the members of their own community on whom was laid the responsibility of transmitting to them the king's words, and having these engraved on stone". We have the case of Sibyrtios as a local ruler of Arachosia during time of Chandragupta and Whsu (Vakshu) a local ruler of Kamboja during time of king Asoka. Since the status of these border nations was midway between provincials proper and the unsubdued borders, the moment these local feudatory rulers found a ripe opportunity to say good-by to their nominal overlords, they did exactly so after the strong arm of king Asoka was withdrawn in 232 BCE. According to Dr R. K. Mukerjee, Dr. Satyaketu Vidyalankar, Dr J. L. Kamboj etc, the Yonas, Kambojas, Gandharas etc became bolder after the powerful arm of king Asoka was withdrawn after 233 BCE and they shook the Maurya yoke off their shoulders. These semi-sovereign border nations were mainly responsible for the eventual break-up and ultimate fall of the Maurya empire. It is possible that Antiochus-Sophagasenus alliance which Polybius, the Greek historian, refers to may have been directed against the Imperial Mauryas of Pataliputra. It may have been designed couple of years prior to 206 BCE since Polybius does allude to Antiochus III's renewal of treaty with Sophagasenus. It appears likely that the Greeks intrigue played a part in the the creation of an independent nation under Sophagasenus and ultimate disintegration of the Maurya empire before the Greek raids. Thus, it seems reasonable to think that on finding the right opportunity to strike, the local ruling chieftain of the Ashavka Kambojas (Paropamisade) broke off with Magadha and carved out an independent kingdom of his own in Kabul/Kapisa valley. We know that since Paropamisade was the heart of Kamboja land, the local ruler for these warlike and freedom loving people naturally may have been a Kamboja background. This may indeed be true since in the Rock Edicts V and XIII which were inscribed only a couple of decades ago, the Kambojas as a feudatory or semi-sovereign (self-ruling) nation finds most prominent position in the edicts of Asoka. The same Kambojas a century earlier had played a very prominent role in the creation of Mauryan Empire by constituting an important component of Chandragupta's army of frontier-highlanders in 324-20 BCE. All this evidence shows that the Kambojas had been very powerful during these centuries. Therefore, looking at time and space propinquity in the context of political scenario during time of Sophagasenus (Subhagasena), one is naturally led to infer that king Sophagasenus must have belonged to the Ashvakan Kshatrya branch of these powerful Kambojas of Kabul/Kapisa region. This view is further reinforced by the fact that the coins of the Ashvaka Kambojas, bearing a legend "Vatasvaka in Brahmi, have been found in north-west frontiers. Dr E. J. Rapson has dated these coins to at least 200 BCE which affirms that the Ashvakas were indeed the powerful rulers on west of Indus around 210/200 BCE and that Indian king Sophagasenus of Polybius may indeed have been an Ashvaka Kamboja ruler. It is also tempting to link the Apraca branch of the kings of Bajaur to king Sophagasenus in this background. Scholars have linked the princes of Apraca dynasty of Bajaur to the Ashvaka clan. And Yuvaraja Kharaosta Kamuio (Kamboja) mentioned in the Mathura Lion Capital appears to be connected with Apraca kings through Apracaraja Indravarman's Silver Reliquary(q.v.). Later when Bactrian Greeks under Demetrius conquered Paropamisade and rest of Afghanistan, the ancestor of Apraca rulers of Kunar/Bajaur finds reference with Greek king Menander in Shinkot reliquary inscriptions found from Bajaur in Kunar.